The present invention relates to coverings impregnated with insecticide for soft furnishings. In particular, the invention relates to coverings impregnated with insecticide, wherein the insecticide is released from the covering over an operational period.
Dust mites live in substantial numbers in places offering warm, humid conditions and a supply of human skin scales and other debris upon which they feed. The surface of a mattress is a particularly attractive habitat and it is understood that the mites move significant distances on and within mattresses in order to seek out and to remain within optimal environmental conditions. The World Health Organisation has identified dust mite concentrations at which genetically predisposed individuals develop antibodies to the house dust mite allergen and concentrations at which there are risks of acute asthma attacks in mite-allergic patients. Thus, it is possible to perform an examination of soft furnishings, such as beds, used by an allergic individual to determine concentrations of house dust mites and to take appropriate action in order to reduce or eliminate these concentrations.
When a permethrin impregnated mattress cover is fitted to a bed, the permethrin formation comes into intimate contact with the surface and sides of the mattress. This close contact, together with the pressure of the occupant of the bed, causes some of the permethrin to move onto the surface of the mattress itself and then subsequently into the surface layers of the mattress. The texture of the mattress cover, in combination with movement between the cover and mattress, results in the permethrin being distributed relatively uniformly within the mattress itself. As the mites move within the mattress, most of them will eventually come into contact with this relatively uniform and continuous zone of permethrin impregnated fabric resulting in the absorption of the chemical into the mite""s body.
Permethrin that has become absorbed or deposited on the mite""s foodstuff may become ingested allowing it to enter into the haemolymph. In addition, while the mite is in physical contact with deposits of permethrin, small quantities of the chemical adhere to the mite resulting in diffusion onto the surface of the mite""s cuticle. Once on the cuticle, the permethrin diffuses directly through the cuticular layers and thereafter passes into the mite""s haemolymph. Once in the haemolymph, the chemical becomes absorbed by the haemolymph lipoproteins resulting in subsequent transportation to the site of action. In addition, permethrin may also diffuse laterally along the trachea of the mite, thereby resulting in it being passed directly to the mite""s nervous system.
The presence of permethrin within the mite""s nervous system results in an increase in the extent to which sodium ions diffuse into the axon of the nerves, resulting in depolarisation. This in turn results in either a spontaneous nerve firing or in the blocking of further action potentials passing along the nerve fibre. The end result of these processes is a disruption in the passage of nervous impulses along the nerve causing either muscular excitation or paralysis, depending upon the stage of the intoxication process.
Disruption of co-ordinated muscle control does not by itself lead directly to the death of the mites but once this control has been lost, a finite period of time will elapse until an essential life sustaining process becomes sufficiently deranged to result in the death of the mite. Thus, a common cause of mite death due to the presence of permethrin is that of failure to control water balance, either internally or by an inability to seek a suitably humid environment.
Patent publication WO 96/28974 discloses the use of a netting impregnated with permethrin and fabricated into a cover appropriate for the covering of domestic articles such as mattresses and duvets etc. Tests in the laboratory suggests that a covering fabricated from the netting disclosed in the aforesaid patent publication should provide protection for a significant period of time when impregnated with a modest quantity of insecticide. However, field trials, conducted under more real life conditions, have shown that the duration over which a net cover provides adequate protection is significantly less than that anticipated by use in the laboratory. Furthermore, tests of this type have also shown that increasing the initial dose of insecticide does not significantly increase the active life of the covering in a proportional way. Furthermore, there is a limit to the extent to which any insecticide (such as permethrin) could be used in a health care situation.
Permethrin is not considered toxic to humans, however overexposure may lead to increased hypersensitivity to touch and sound, tremors and convulsions. Contact with permethrin may produce skin sensations such as numbing, burning or tingling but these are reversible and usually subside within a period of twelve hours. When placed directly in contact with the skin, tests have shown that about 0.5 percent of the chemical is absorbed by the skin, therefore care should be taken so as to minimise human exposure while maintaining the pesticide effect, as in any pesticide use.
It is an object of the present invention to increase the operational period over which a covering impregnated with insecticide is effective, without being required to increase initial insecticide concentrations.
According to a first aspect of the present invention, there is provided a covering for soft furnishing, impregnated with insecticide wherein said insecticide is released from said covering over an operational period so as to encourage the absorption of said insecticide into said soft furnishings, comprising a covering manufactured from machined fabric having interstices sufficiently small to reduce the rate of insecticide release over said operational period.
In a preferred embodiment, the covering is configured to be applied to mattresses, duvets, pillows or other bedding elements.
Preferably, the insecticide is a synthetic pyrethroid such as deltamethrin, sypermethrin, allethrin or bifenthrin and in a preferred embodiment the synthetic pyrethroid is permethrin.
In a preferred embodiment, the fabric is machined from polyester yarn, preferably having a gauge in the range of twenty to one hundred decitex. Preferably the interstices of the fabric are smaller than that provided by machined netting and in a preferred embodiment, the machined fabric is a knitted voile. Preferably, the knitted voile has a weight of between thirty-five to forty-five grams per square meter and contains between four hundred to seven hundred milligrams of insecticide (preferably permethrin) per square meter.
According to a second aspect of the present invention, there is provided a covering for soft furnishings, impregnated with permethrin with a loading of between five hundred and six hundred milligrams per square meter and configured to release permethrin over an operational period of between one-and-a-half and two-and-a-half years to give a final loading of between one hundred to two hundred milligrams per square meter.
Preferably, the covering is fabricated totally or in part of knitted voile and said voile may be knitted from polyester yarn.
According to a third aspect of the present invention, there is provided a method of producing a covering for soft furnishings configured to provide protection against house dust mites, comprising the steps of knitting a voile from a polyester yarn; machining a cover from said knitted voile; and impregnating said machined cover with an insecticide.
In a preferred embodiment, the machined cover is impregnated by being immersed in an impregnation fluid and then rolled between rollers to control the level of fluid pick-up. Preferably, the rolled voile is passed through drying means to remove water from the insecticide.
In a preferred embodiment, the impregnation fluid is a suspension of permethrin in water and the impregnation fluid may be mixed by adding permethrin in organic solution to water to provide the required suspension. Preferably, the organic solution contains from five to fifty percent permethrin and between fifty and ninety millimeters of organic solution may be added to each liter of water.
Preferably, an insecticide loading of between four hundred and seven hundred milligrams per square meter is achieved by a wet pick-up of between fifty to seventy percent. Preferably, the insecticide is permethrin.